That was the subject line on a Facebook message to Lena Dunham from her ex-boyfriend's mother. "Nancy" was writing to say: "It's time to sever the Facebook connection so I'm going to block you. We wish you all the BEST!"

Ms. Dunham, creator of HBO's hit show Girls, describes the unnerving experience in a New Yorker essay called First Love. Published earlier this month, the piece shreds Nancy, as well as the ex-boyfriend, Noah. (All names were changed, although Ms. Dunham doesn't shy away from identifying details, like Nancy's habit of pouring hot clarified butter into her eyes, an "Ayurvedic tradition.")

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Ultimately, Nancy's note rattled Ms. Dunham, who blasted Noah for his mom's tactics and then promptly shuttered her Facebook and Twitter accounts in shame.

Her New Yorker essay left readers aghast at Nancy's poor etiquette. Ms. Dunham's own mother was vexed: "How wrong! That woman is a grown-up, and you are a child," she said to her daughter at the time.

With all the inevitable mortification, why do parents ever risk contacting their children's exes? The Globe asked Terri Apter, Cambridge University psychology professor and author of Difficult Mothers: Understanding and Overcoming Their Power, and Laura Baron, life coach on A&E's Monster In-Laws, to discuss why parents go off on their brood's exes – and what they should consider before hitting send.

Why parents lose it

Parents suffer the breakup or divorce by proxy and "may be frightened and disappointed by the changing configuration of the family," says Dr. Apter. "Families live under a shared emotional skin. An insult to one family member – particularly to your child – is felt by others."

The full story?

Dr. Apter says parents might not be getting the entire picture from their children: "Parental bias excludes empathy for anyone outside the bloodline." She says there may be projection, or self-justifying criticism: "If my son or daughter is treating you badly, then you must deserve it."

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Bruised parental egos

"What's in it for you?" said Ms. Baron. "Is it actually your ego that's been hurt? It's a question parents need to ask themselves continually as they start to 'ego-parent,' where they push their kids to do things for their own internal satisfaction." This is where boundaries are crossed: "Parents need to understand it isn't their relationship – they had their shot."

Let Noah throw his own punches

Ms. Baron says the net effect of parental meddling is always embarrassment for the son or daughter: "What does it say about what the parent thinks of the child? By trying to make a point for them, they're not allowing the kid to go through their natural process of feeling."

Needling, passive-aggressive Facebook wall posts can actually foment more contact between your child and the baddie ex, as it did in Ms. Dunham's case: "It can push their son or daughter back together with the person they've severed ties with. It causes further strife and undermines what your kid thought was right for them," says Ms. Baron.

Take a breather

Dr. Apter suggests livid parents ask themselves what they can gain or lose by responding angrily. "Be pragmatic and identify your aims," she said. "Under anger's spell, we often long for some kind of revenge. There is no point to this battle. The rough guide to the power of in-laws suggests you take the long view, reduce expectations and wait to see the fallout."

Don't get too close to "next"

"When you're meeting your kid's next [partner], consider that it is simply their 'next,'" says Ms. Baron. "This isn't the person you're supposed to invest all of your friendship and love in. You can get close, but family isn't family until they've put a ring on it, and even then …" Her voice trails off ominously.

Facebook blocking is silent

Want to unfriend or block a child's former paramour? No need to send a missive detailing the act. Speaking of "Nancy," Ms. Baron says: "This was not done to unfriend Lena. This was done to make a point."

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